nickle



Aug. 1, 1933. c. A. NICKLE 1,920,754

ELECTRICAL INSTRUMENT Filed Oct. 19. 1951 Inventor-- CliffordANickls,

His Attorney Patented Aug. 3, i933 ELECTRECAL rus'rapiuanr I Clifford A.Nickle, Schenectady, N. it, assiglnor to General Electric Company, aCorporation of New York Application October 19, 1931. Serial No. 569,616

8 Claims.

My invention relates to electrical instruments and dynamo-electricdevices and in particular to devices employing a magnetic field producedby a permanentmagnet.

An object of my invention is the production of electrical devices ofdecreased size and weight for a given capacity. A more specific objectof my invention is the production of electrical instruments of decreasedsize and weight and increased stability without loss of sensitivity. Afurther object of my invention is the production of inherently shieldedcompact instruments. Another object of my invention is the provision ofan electrical instrument which may be quickly and convenientlymagnetized.

In accordance with my invention I provide a current conducting coil anda core therefor which is permanently magnetized in a directiontransverse to its axis. Means are provided for the relative rotation ofthe permanent magnet with respect to the current conducting coil or viceversa. In place of the external permanent magnet usually used in devicesof this kind I surround the coil and its magnetized core with a softiron ring which provides a return path for the lines ofmagneticinduction and inherently shields the device from externalmagnetic fields. The magnetized core is preferably composed of a highgrade permanent magnet material such as cobalt steel which may bemagnetized to a high intensity and retains its magnetism with greatstability. The features of my invention which I believe to be novel andpatentable are pointed out in the appended claims.

In order to obtain a better understanding of my invention referencemaybe had to the accompanying drawing in which Fig. 1 represents anelevation partly in section of an embodiment of my invention taking theform of an indicating electrical instrument, Fig. 2 is a cross-sectionof the instrument shown in Fig. 1, taken on line 2-2; Fig. 3 is aschematic diagram illustrating the relation between the magnetic pathsand the coil, and Fig. 4 represents a modification arranged as acontact-making instrument.

Referring now more in detail to the drawing in which like referencecharacters refer to like parts throughout, 1 provide a movable coil 11surrounding a permanently magnetized core 12, both of which aresurrounded by the magnetic shield 13 which is preferably of soft iron.To

further shield the instrument and to protect the moving element againstair currents and mechanical injury I may also provide soft iron plates23. The magnetized core 12 may be composed of cobalt steel or otherhighly retentive material and is magnetized in a direction transverse tothe axis of rotation of the coil 11.

The coil 11 is carried by a shaft 14 supported by the bearings 15 and 16mounted upon the (Cl. ill-$5) Although I have shown the core 12 with avertical hole coaxial therewith in order to permit the passage of theshaft 14 through the core it will be understood that the permanentmagnet might also be solid and the coil 11 might be provided with stubshafts instead of a single shaft extending from bearing 15 to hearing16.

In order to obtain the maximum lightness of v the ,moving parts, andconsequently the maximum sensitivity, I prefer to mount the coil 11 asthe rotatable element and the permanent magnet 12 as a stationaryelement but it will be understood that any method of mounting may beemployed in which relative rotation is permitted between the currentconducting coil 11 and the permanent magnet 12.

From Fig. 3 it will be seen that this method of construction providesthe maximum efiiciency of the permanent magnet since the magnetic fluxis confined to the air gap of the instrument. It will be understood thatthe air gap between the permanent magnet 12 and shield 13 may be made assmall as is consistent with the mechanical limitations imposed by therequirement that coil 11 shall be freely rotatable in the space betweenpermanent magnet 12 and magnetic shield 13. Since this air gap may bemade as small as thatin the dArsonval instruments employing an externalpermanent magnet and since the area of the air gap is increased to thatof the entire cylindrical surface of permanent magnet 12 it will beunderstood that a very great field inten sity may be obtained in the airgap for a given strength of the magnet. The parts 12' and 13 are shownconcentric and the air gap uniform. but the invention is not limited tothis exact arrangement.

I have found that an instrument constructed as here shown may veryconveniently be magnetized by placing the instrument completelyassembled with its magnetic shield 13 between the poles of anelectromagnet furnishing a strong magnetic. field. Preferably I employabout 40.000 ampere turns in the electromagnet when magnetizing theinstrument" in this manner. Such a high field strength completelysaturates the shield 13 permitting lines of force to pass through andmagnetize the core 12. By using cobalt steel, for example, an alloywhich is about 46% cob'alt'I find that the permanent magnet may bemagnetized in a single operation to the desired strength and that thepermanent magnet will retain this strength with great stability. I

have not found it necessary to resort to aging of the permanent magnetor to over-magnetization initially, followed by a demagnetizing processin order to obtain stability of the permanent magnet. I have alsofoundthat my instrument is not injured magnetically by allowing it to besubjected to a field of excessive strength or to an alternating-currentfield after it has been calibrated.

It will be obvious that electrical instruments constructed in the mannerhere shown have the advantage of very materially reduced size and weightover instruments employing the usual form of exterior horseshoepermanent magnet, and I have found that the sensitivity of theinstrument is not impaired as compared to the constructions employingexterior permanent magnets. Since the instrument is inherently shieldedagainst external fields it has a further advantage over instrumentsemploying external permanent magnets when it is desired to produce afully shielded instrument.

Although I have explained the principle of my invention in connectionwith a measuring instrument, it will be understood that my invention isnot limited thereto but includes any device in which\ a permanent magnetand a current conducting coil are arranged in inductive relation or arerelatively movable. For example, Fig. 4 illustrates one form of a relayin which the pointer 21 carries a contact 25 cooperating with a pair ofcontacts 26. Obviously my invention also includes recording instrumentsand currentresponsive instruments of many types including not onlyvoltmeters and ammeters but also instruments utilizing compound coils,ratio instruments and other devices utilizing crossed coils and anyother instruments in which permanent magnetic fields are used.

Obviously my invention is not limited to devices in which the relativerotation between the coil and the permanent magnet is restricted to afraction of a revolution, but may also be utilized in magnetos and otherdevices in which a continuous rotation takes place between a permanentmagnet and a current conducting coil.

While I have described my invention in concrete form and as operating ina specific manner in accordance with the provisions of the patentstatutes, it should be understood that I do not limit my inventionthereto since various modifications thereof will suggest themselves tothose skilled in the art without departing from the spirit and scope ofmy invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A current-responsive instrument comprising in combination, a currentconducting coil, a shaft rotatably supporting said coil, and a permanentmagnet of substantially circular cross section magnetized in a directiontransverse to its axis, and having a coaxial opening therein to permitsaid shaft to be mounted substantially in the axis of said magnet, saidcoil surrounding said magnet so as to be in inductive relationtherewith.

2. A current-responsive instrument comprising in combination, arotatable current conducting coil and a permanent magnet composed ofcobalt steel, said'magnet having a substantially circular cross section,being laterally supported at only one side within said coil and beingmagprising relatively high coercive force material, 3i

a shield comprising relatively permeable material, surrounding andspaced from said magnet and presenting a return path for the lines ofmagnetic induction passing through said magnet, non-magnetic meansattaching one side of 9 said magnet to and spacing it from thecorresponding side of said shield, and a current conducting coil occupyg a portion of the space between said magnetand said shield, said magnetand said coil being mounted to permit relative 9 motion between saidcoil and magnet.

4. A torque producing element comprising a permanent magnet composed ofa material retaining a relatively high intensity of magnetization, and arotatably defiectable rotatable current conducting coil surrounding saidpermanent magnet in inductive relation therewith, said permanent magnetbeing magnetized in a direction transverse to the axis of rotation ofsaid coil and having a surface conforming in shape to the surfacegenerated by the deflection of said coil.

5. A current-responsive instrument comprising a permanent magnetcomprising relatively high coercive force material substantiallysymmetrical with respect to a given axis and magnetized transverselythereto, a current conducting coil mounted to permit relative motionwith respect to the magnet, and a magnetic shield spaced from andsurrounding said parmanent magnet, said coil occupying the space betweensaid shield and said magnet.

6. A current-responsive instrument comprising a substantiallycylindrical-transversely magnetized permanent magnet comprising amaterial of relatively high coercive force, a substantially annularmagnetic shield spaced therefrom and coaxial therewith, and a currentconducting coil occupying the space between said shield and u saidmagnet, and rotatable about their common axis. I

7. An electrical relay comprising a rotatable current -conducting coil,a contact-making element controlled thereby, a stationary core withinsaid coil comprising a material of relatively high coercive forcepermanently magnetized transversely 41o the axis of rotation of saidcoil, and conforming substantially in shape to the space circumscribedby the rotation of said coil, and a substantially annular stationaryshield surrounding said core and coil.

8. An electrical measuring instrument comprising a transverselymagnetized stationary cylindrical permanent magnet comprising a materialof relatively high coercive force, a stationary annular magnetic shieldspaced therefrom and coaxial therewith, and a current-conducting coilmounted to rotate within the space between said magnet and shield abouttheir common axis.

CLIFFORD A. NICKLE.

